A hybrid radiation detector for simultaneous spatial and temporal dosimetry

In this feasibility study an organic plastic scintillator is calibrated against ionisation chamber measurements and then embedded in a polymer gel dosimeter to obtain a quasi-4D experimental measurement of a radiation field. This hybrid dosimeter was irradiated with a linear accelerator, with temporal measurements of the dose rate being acquired by the scintillator and spatial measurements acquired with the gel dosimeter. The detectors employed in this work are radiologically equivalent; and we show that neither detector perturbs the intensity of the radiation field of the other. By employing these detectors in concert, spatial and temporal variations in the radiation intensity can now be detected and gel dosimeters can be calibrated for absolute dose from a single irradiation

Evaluation of volumetric modulated arc therapy (VMAT) with Oncentra MasterPlan® for the treatment of head and neck cancer

Background Several comparison studies have shown the capability of VMAT to achieve similar or better plan quality as IMRT, while reducing the treatment time. The experience of VMAT in a multi vendor environment is limited. We compared the plan quality and performance of VMAT to IMRT and we investigate the effects of varying various user-selectable parameters. Methods IMRT, single arc VMAT and dual arc VMAT were compared for four different head-and-neck tumors. For VMAT, the effect of varying gantry angle spacing and treatment time on the plan quality was investigated. A comparison of monitor units and treatment time was performed. Results IMRT and dual arc VMAT achieved a similar plan quality, while single arc could not provide an acceptable plan quality. Increasing the number of control points does not improve the plan quality. Dual arc VMAT delivery time is about 30% of IMRT delivery time. Conclusions Dual arc VMAT is a fast and accurate technique for the treatment of head and neck cancer. It applies similar number of MUs as IMRT, but the treatment time is strongly reduced, maintaining similar or better dose conformity to the PTV and OAR sparing

Спектральный анализ звуков кашля у больных COVID-19

Cough is a frequent manifestation  of COVID-19  (COronaVIrus Disease 2019), therefore,  it has an important  diagnostic value. There is little information  about the characteristics  of cough of COVID-19  patients in the literature.  To perform a spectral analysis of cough sounds in COVID-19 patients in comparison  with induced cough of healthy individuals. Methods. The main group consisted of 218 COVID-19  patients (48.56% – men, 51.44% – women, average age 40.2 (32.4; 50.1) years). The comparison group consisted of 60 healthy individuals (50.0% men, 50.0% women, average age 41.7 (31.2; 53.0) years) who were induced to cough. Each subject had a cough sound recorded,  followed by digital processing using a fast Fourier transform algorithm. The temporal-frequency parameters of cough sounds were evaluated: duration (ms), the ratio of the energy of low and medium frequencies (60 – 600 Hz) to the energy of high frequencies (600 – 6 000 Hz), the frequency of the maximum sound energy (Hz). These parameters  were determined  in relation  to both the entire cough and individual phases of the cough sound. Results. Significant differences were found between some cough parameters  in the main group and in the comparison  group. The total duration  of the coughing act was significantly shorter in patients with COVID-19, in contrast to the induced cough of healthy individuals (T = 342.5 (277.0; 394.0) – in the main group; T (c) = 400.5 (359.0; 457.0) – in the comparison  group; p = 0.0000). In addition,  it was found that the cough sounds of COVID-19  patients are dominated by the energy of higher frequencies as compared  to the healthy controls (Q = 0.3095 (0.223; 0.454) – in the main group; Q (c) = 0.4535 (0.3725; 0.619) – in the comparison  group; p = 0.0000). The maximum frequency of cough sound energy in the main group was significantly higher than in the comparison  group (Fmax = 463.0 (274.0; 761.0) – in the main group; Fmax = 347 (253.0; 488.0) – in the comparison  group; p = 0.0013). At the same time, there were no differences between the frequencies of the maximum energy of cough sound of the individual phases of cough act and the duration of the first phase. Conclusion. The cough of patients with COVID-19 is characterized  by a shorter duration and a predominance of high-frequency energy compared to the induced cough of healthy individuals.Кашель – частое проявление заболевания, вызванного  новой коронавирусной инфекцией COVID-19  (COronaVIrus Disease 2019), следовательно,  он имеет важную диагностическую ценность.  В доступной  литературе обнаружено  крайне  мало сведений,  характеризующих звуки кашля у больных COVID-19.  Целью исследования явился  спектральный анализ звуков кашля у больных COVID-19  в сравнении с индуцированным кашлем  у здоровых  лиц.  Материалы и методы. Основную  (1-ю)  группу составили  больные  COVID-19  (n = 218: 48,56 % – мужчины,  51,44 % – женщины; средний  возраст – 40,2 (32,4; 50,1) года). Группу сравнения (2-ю) составили  здоровые лица (n = 60: 50,0 % – мужчины,  50,0 % – женщины; средний  возраст – 41,7 (31,2; 53,0) года) с индуцированным кашлем.  У каждого пациента проводилась  регистрация звуков кашля  с последующей  цифровой обработкой  с помощью  алгоритма  быстрого  преобразования Фурье. Оценивались временно-частотные параметры  звуков кашля  – продолжительность (мс),  отношение энергии  низких  и средних частот (60–600 Гц) к энергии  высоких частот (600–6 000 Гц), частота максимальной энергии  звука (Гц). Указанные  параметры  определялись как в отношении всего кашля,  так и его отдельных фаз звука. Результаты. У пациентов 1-й и 2-й групп установлены  некоторые достоверные различия параметров кашля. Общая продолжительность кашлевого акта (T) оказалась значимо меньше у больных COVID-19, в отличие от индуцированного кашля у здоровых лиц (T = 342,5 (277,0; 394,0) – в 1-й группе; T (c) = 400,5 (359,0; 457,0) – в группе сравнения; p = 0,0000).  Также  выявлено, что в звуках кашля  у больных  COVID-19  преобладает  энергия  более  высоких  частот  (Q) по сравнению с таковой  у здоровых  (Q = 0,3095 (0,223; 0,454) – в 1-й группе и Q (c) = 0,4535 (0,3725; 0,619) – в группе сравнения; p = 0,0000).  Максимальная частота  энергии  звуков  кашля  (Fmax)  в 1-й  группе  была  достоверно  выше,  чем у лиц  группы  сравнения (Fmax = 463,0 (274,0; 761,0) – в 1-й группе; Fmax  = 347 (253,0; 488,0) – в группе сравнения; p = 0,0013). При этом различий  между частотами максимальной энергии звуков кашля отдельных фаз кашлевого акта и продолжительности 1-й фазы кашля не выявлено. Заключение. Кашель у больных COVID-19 отличается меньшей продолжительностью и преобладанием энергии высоких частот по сравнению с таковыми у здоровых лиц с индуцированным кашлем

Beam perturbation characteristics of a 2D transmission silicon diode array, Magic Plate

The main objective of this study is to demonstrate the performance characteristics of the Magic Plate (MP) system when operated upstream of the patient in transmission mode (MPTM). The MPTM is an essential component of a real-time QA system designed for operation during radiotherapy treatment. Of particular interest is a quantitative study into the influence of the MP on the radiation beam quality at several field sizes and linear accelerator potential differences. The impact is measured through beam perturbation effects such as changes in the skin dose and/or percentage depth dose (PDD) (both in and out of field). The MP was placed in the block tray of a Varian linac head operated at 6, 10 and 18 MV beam energy. To optimize the MPTM operational setup, two conditions were investigated and each setup was compared to the case where no MP is positioned in place (i.e., open field): (i) MPTM alone and (ii) MPTM with a thin passive contamination electron filter. The in-field and out-of-field surface doses of a solid water phantom were investigated for both setups using a Markus plane parallel (Model N23343) and Attix parallel-plate, MRI model 449 ionization chambers. In addition, the effect on the 2D dose distribution measured by the Delta4 QA system was also investigated. The transmission factor for both of these MPTM setups in the central axis was also investigated using a Farmer ionization chamber (Model 2571A) and an Attix ionization chamber. Measurements were performed for different irradiation field sizes of 5 x 5 cm2 and 10 x 10 cm2. The change in the surface dose relative to dmax was measured to be less than 0.5% for the 6 MV, 10 MV, and 18 MV energy beams. Transmission factors measured for both set ups (i & ii above) with 6 MV, 10 MV, and 18 MV at a depth of dmax and a depth of 10 cm were all within 1.6% of open field. The impact of both the bare MPTM and the MPTM with 1 mm buildup on 3D dose distribution in comparison to the open field investigated using the Delta4 system and both the MPTM versions passed standard clinical gamma analysis criteria. Two MPTM operational setups were studied and presented in this article. The results indicate that both versions may be suitable for the new real-time megavoltage photon treatment delivery QA system under development. However, the bare MPTM appears to be slightly better suited of the two MP versions, as it minimally perturbs the radiation field and does not lead to any significant increase in skin dose to the patient